The present invention relates to a security ink for use in a letterpress printing process, and more particularly, to a security ink including a fluorescent pigment therein which may be activated under ultraviolet light to authenticate security documents such as checks, birth records, auto titles, and the like.
Inks for use in letterpress printing processes are well known in the art. Such inks generally comprise a colored pigment and a colored dye which are typically printed as series of numbers or account numbers on security documents such as checks. When such inks are printed on a substrate by letterpress techniques, the colored pigment stays on the surface of the substrate, while the colored dye at least partially penetrates the surface to form a visible image on the reverse side of the substrate. Such a "dual-component" ink provides a security feature in that one cannot easily alter the images on the substrate because of the penetration of the colored dye into the reverse side of the substrate.
Security documents which utilize such dual-component inks to provide numbering are also generally printed with variable or nonvariable information such as names, amounts, etc. which are typically added by mechanical impact printing devices. However, with the advance of microcomputer technology, a number of faster printing methods have been developed to take advantage of the high-speed printing output which is now possible. Laser printers are an example of non-impact printers which are faster, quieter, and more reliable than impact printers. However, it has been found that dual-component letterpress inks are unsatisfactory for use with laser printers as the inks are not heat resistant and cannot be passed through a laser printer without causing damage to the images formed by the inks.
In recent years, it has also become an increasing concern to be able to provide additional security or authentication features to such inks. For example, many security inks in use today have incorporated fluorescent compounds therein which may be activated under ultraviolet light so as to provide an authentication feature or to provide evidence of attempted tampering. However, such fluorescent compounds have not been successfully used in conjunction with letterpress numbering inks as such fluorescent pigments tend to be masked by the other pigments in the ink.
Accordingly, there is still a need in the art for an ink for use on security documents which may be passed through a laser printer without damage and which includes one or more security and/or authentication features.